Dimeric poly-n-vinyl carbazole organic photoconductor and photoconductive elements embodying same

ABSTRACT

THE INVENTION IS ADDRESSED TO THE PREPARATION OF AN ELECTROPHOTOGRAPHIC ELEMENT HAVING A PHOTOCONDUCTIVE LAYER FORMULATED OF AN ORANIC PHOTOCONDUCTOR IN THE FORM OF AN ALKENYL CARBAZOLE DIMER AND IN WHICH THE ELECTROPHOTOGRAPHIC ELEMENT CAN BE PROCESSED FOR IMAGING PURPOSES IN THE CONVENTIONAL MANNER FOR ELECTROSTATIC PRINTING.

8- 1972 A. J. GUARNACCIO 3.534.

DIMERIC POLY'N-VINYL CARBAZOLE ORGANIC PHOTQCQNDUCTQR ANDPHOTOCONDUCTIVE ELEMENTS EMBODYING SAME Filed Aug. 24, 1970 FIG. 1

United f States Patent Oflice r 3,684,506 Patented Aug. 15, 1972 (Filedunder Rule 47(a) and 35 U.S.C. 116) Int. Cl. G03g 5/06 U.S. c1. 961.6Claims ABSTRACT on THE, DISCLOSURE The invention is addressed to thepreparation of an electrophotographic element having a photoconductivelayer formulated of an organic photoconductor in the form of an alkenylcarbazole dimer and in which the electrophotographic element can beprocessed for imaging purposes in the conventional manner forelectrostatic printing.

This is a continuation-in-part of copending application Ser. No.612,432, filed Jan. 30, 1967, now abandoned.

This invention relates to an electrophotographic composition andmaterial and to a photoconductive coating formed thereof for use in thepreparation of an image by electrostatic or xero'g'raphic technique. 1

A well known electrostatic imaging process, generally referred to as theXerox process and described in the Carlson Pat. No. 2,297,691, involvesan element-carrying a photoconductive layer which is given a blankelectrostatic charge under subdued light or in the dark, as by iontransfer from a corona discharge, followed by an exposure to lightmodulated by an image, as by projection of a photographic image. Theilluminated areas of the charged photoconductive layer aredischarged toleave a latent electrostatic image on the layer. The resultantelectrostatic image can then be developed, as by dusting with anelectroscopic powder, such as a pigmented resinous powder carrying anopposite electrostatic charge, as described in US. Pats. Nos. 2,618,551;2,788,288; or 2,940,934. Instead, development can be achieved by aliquid developer of the type described in US. Pats. Nos'. 2,877,133,2,891,911, and

2,907,674. The powder or pigment of the powder or liquid developeradheres to the electrostatically charged latent image; The resultingdeveloped image can be used in a number of ways. It can be fixed thereonto form the image on the photoconductive layer or it can be transferredfrom the photoconductive layer to a copy sheet for fixing. A widely usedelectrostatic process, such as described in the Grieg Pat. No,3,052,539, or in the Middleton Pat. No. 3,121,006, utilizes as theelectrophotographic element ordinary paper as the conductive base havingaphotoconductive coating of zinc oxide which forms a layer having aconductivity'of at least 10- oh'mcm.'' in the absence of illuminationand adecay factor of less than 3.0.

Such inorganic photoconductors are limited in their application and use.For example, the applied coatings are not transparent and they are thuslimited in their manner of exposure to produce the latent electrostaticimage. In order to achieve copy of good quality, it is necessary for thephotoconductive coating of inorganic photoconductors to be provided inheavy coating weights thereby to increase the cost of the coating andmaterially to increase the weight and stiffness of the sheet. Inaddition, layers formed of inorganic photoconductors are handicapped bysurface sensitivity to hard objects.

It is an object of this invention to produce an electrophotographicmaterial formulated of an organic substance which can be formulated toproduce a new and improved photoconductive layer which can be employedin layers of low coating weight; which is relatively translucent ortransparent to light; which has little surface sensitivity to hardobjects; which can be used in conventional electrostatic copyingprocesses for the preparation of latent electrostatic images that can bedeveloped to produce copy of good quality; in which the coating can beapplied in a simple and efficient manner to produce a photoconductivelayer having good shelf life and the desired resistivity for use inelectrostatic reproduction; which can be formulated as a stable solutionin a solvent system; which produces a photoconductive layer that is freeof flaking; which is characterized by slow dark decay; which produces aphotoconductive layer useful in electrophotography, photoplasticrecording, photographic recording and as a lithographic duplicatingmaster.

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, an embodiment of this invention is shown in the accompanyingdrawing, in which FIG. 1 is a perspective view, partially in section, ofa photoconductive element embodying the features of this invention;

FIG. 2 is a perspective view similar to that of FIG. 1 showing thephotoconductive element with the latent electrostatic image formedthereon; and

FIG. 3 is a view similar to that of FIGS. 1 and 2 showing thephotoconductive element with the image fixed thereon.

It has been found that a dimer of N-alkenyl carbazole can be used as anorganic electrophotographic material in the preparation ofphotoconductive coatings employed in electrostatic copy processes inwhich the dimer of N-alkenyl carbazole is represented by the formula:

wherein R is hydrogen; an alkyl group such as methyl, ethyl, propyl,isopropyl, butyl, pentyl-up to dodecyl; an aryl group such as benzyl,naphthyl, phenanthryl, anthracyl and the like; a cycloalkyl group suchas cyclopentyl,

cyclohexyl and the like; an alkylaryl group such as xylyl,

tolyl, and the like; a cyano group, a carboxylic group or an aminogroup,and in which R is hydrogem'an alkyl group, an aryl group or a cycloalkylgroup of the type described above for R In a preferred compound, both R,and R are hydrogen.

' The dimers of N-alkenyl carbazoles described above nol in a ratio ofabout 9 parts by weight methanol to 1 part by weight water, and ferricnitrate is added. After a few minutes, a crystalline precipitate isformed by the reaction.

Fe (Nom 1 aq. methanol wherein R and R are as described above.

It has been found that electrophotographic coatings formulated toinclude one of the foregoing dimers and a binder can be charged by wayof, for example, a corona discharge at a faster rate than organicphotoconductors heretofore employed, such as polyvinyl carbazole, whenused in an electrostatic copy process.

The organic photoconductive dimer of N-alkenyl carbazole is formulatedwith a suitable binder for application to form the photoconductivecoating on a suitable conductive base sheet 12 such as paper, metal,film, and the like.

As the binder component with which the dimer is combined, use should bemade of a material which has a specific conductivity greater than 10-ohmcm.- and preferably higher than 10- ohmcm.- As a representative, itis preferred to make use of a Union Carbide Corporation resinidentified. as VMCH formulated of 86% vinyl chloride, 13% vinyl acetateand 1% maleic acid, but other resinous binders can be employed, such asbutadiene-styrene copolymer 45:55, organo silicon resins, such asDow-Corning DC-996, a polystyrene, acrylic and methacrylic esterpolymers, such as Acryloid A-10, chlorinated rubber, such as Parlon, andalkyd resins, such as General Electric Glyptol 2469.

In the combination of dimer and resin, the materials can be employed inthe ratio of 1 part by weight dimer to ganic solvent, such as theketones, esters and aromatic hydrocarbons, in which a desired coatingviscosity can be achieved with a solid content within the range of 525%by eight.

By way of modification, the light sensitivity of the dimer can beincreased by the combination to include electron aflinitive molecules,such as tetracyanoethylene, chloranil and the like; acid activators,such aslcarboxylic acids; mineral acids, such as hydrochloric acid,nitric acid and the like, or metal halides, such as boronjchlorides,phosphorus chlorides and the like; and chemical activators, such asiodoform, carbon tetrabromide and carbonyl containing compounds, such asbenzophenone, hydroxybenzophenone and the like. The desired increase inlight sensitivity can be achieved when the electron affinitive compoundis incorporated into the coating in an amount within the range of 0.005to 1.0 percent'by weight on a solids basis. By way of still furthermodification, the spectral sensitivity of the dimer can be extended intothe visible part of triaryl methane dyes, xanthene dyes, thiazine dyes,acrithe spectrum by the addition of dye sensitizers', such as dine dyes,and the like. For this purpose, it is desirable to make useof a dyesensitizer-inan amount-:within the range of 0.005 to 1.0 percent byweight of the coating on a solids basis.

The following are examples of coating compositions embodying thefeatures of'this' invention and which may be applied on a suitableconductive base sheet, such as paper to produce an electrophotographicelement capable of being imaged by conventional electrostatic technique.

,EXAMPLEI N-vinyl carbazole dimer g 1.0

Vinyl "chloride (86)-vinyl acetate (l3) -maleic acid (1) resin (VMCH) g1.0 Methylene chloride solvent cc 20 EXAMPLE 2 t N-vinyl carbazole dimerg 1.0 VMCH resin g 1.0 Methylene chloride solvent cc 20 1 %-solution inmethanol of Rhodamine B dye; -cc-.. 0.5

' X PL N-propenylcarbazole dimer g 1.0 Silicone resinDow DC-996 H-. g1.0 Toluene ..cc 20 1% solution of chloranil cc 0.5

EXAMPLE 4 N-styryl carbazole dimer g 1.0 Polyvinyl acetate resin g "1.0Acetone cc Y 20 Dichloroacetic acid cc 0.0002 Rhodarnine dye" cc 0.0002

The composition. of Examples 1 to 4 is coated onto the surface of asuitable base sheet, such as paper, by conventional coating techniques,such as flow coating, roller coating and the like. The amount of coatingapplied can bevaried over a fairly wide range although it is preferableto make useof a relatively light coating such as a coating weight withinthe range of, A to 10 pounds per-3,000 square feet of surface area andpreferably of about /2 to 5 pounds per 3,000 square feet of surfacearea. The applied coating can be allowed to air dry but drying can beaccelerated by exposure of the coated sheet to elevated temperature inthe order of -250 F. 1

The layer 10 that is formed on the base sheet 12 is a goodphotoconductive coating which will accept and retain an overallelectrostatic charge when sprayedby corona discharge from a conventionalsource under. sub,- dued light. When the charged layer is exposed tolight, the charge becomes dissipated in the exposed portions 14 and isretained in the unexposed portions to define a latent electrostaticimage 16 which-can be developed by, conventional liquid or powderdevelopers of the types previously described. The organicphotoconductorperrnits exposure to be made by reflex or by shoot-throughas well as projection to produce the latent electrostatic image forsubsequent development. I 1 V The developed image 18 .can be. seton the.layer for direct. copy or the powdered image can betransferred to acopy sheet by charge reversal or by direct contact whereafter the imageis set on the copy sheet. When the photoconductive layer isapplied-onto-the surface, of a suitable lithographic rnaster,.animaged'master can be produced. when thei'developed image. is set onthe plate or the powdered imagev can be transferredfromthephotoconductive layer to the surface of a lithographic plate for imagingthe duplicating master for use in the production of multiple copies bylithographic duplicating technique. t

Thus, in use, the coated sheet is first bombarded in subdued light bycorona discharge to spray the surface of the layer'with an electrostaticcharge. The charge is received and held by the photoconductive coating10. The charged sheet is then exposed to light modulated by projectionof a photographic image whereby the photoconductive coating is renderedconductive in the exposed areas to enable dissipation of theelectrostatic charge while the charge is retained in the unexposed areasto define the latent electrostatic image 16.

The imaged layer is then dusted with a developing electroscopic powderor by a liquid developer whereby the pigmented resinous particles of thedeveloping composition are attracted to the latent electrostaticimagefor development. The particles can be set by heat to fix the image 18 ortransferred to a copy sheet for setting thereon.

It will be apparent that we have provided anew and improvedelectrophotographic element which can be used in electrostatic copyprocesses for the development of images by electrostatic technique.

It will be further understood that changes may be made in the details offormulation and construction without departing from the spirit of theinvention, especially as defined in the following claims.

We claim:

1. An electrophotographic recording element comprising a base sheet anda coating on the surface of the base sheet containing an organic binderand an alkenyl carbazole dimer having the formula:

in which R is a group selected from the group consisting of hydrogen,alkyl, aryl, cycloalkyl, alkylaryl, cyano, carboxyl and amino and R is agroup selected from the group consisting of hydrogen, alkyl, aryl andcycloalkyl.

2. An electrophotographic claimed in claim 1 in which the alkenylcarbazole dimer is present in the coating in combination with an organicbinder having a specific conductivity of at least 10 ohm" cmf 3. Anelectrophotographic recording element as claimed in claim 1 in which theorganic binder and alkenyl carbazole dimer are present in the coating inthe ratio of 1 part by weight dimer to 0.l-l parts by weight binder.

4. An electrophotographic recording element as claimed in claim 2 inwhich the coating includes a compound that broadens the spectralsensitivity of the dimer, said compound being selected from the groupconsisting of triaryl methane dye, xanthene dye, thiazine dye andacridine dye, said compound being present in an amount within the rangeof 0.005 to 1.0 percent by weight of the coating.

5. An electrophotographic recording element as claimed in claim 2 inwhich the coating includes a compound to increase the light sensitivityof the dimer, said compound selected from the group consisting oftetracyanoethylene, chloranil, a carboxylic acid, a mineral acid, anacidic metal halide, iodoform, carbon tetrabromide, benzophenone andhydroxy benzophenone, and being present in an amount sufiicient toincrease the light sensitivity of the dimer.

6. An electrophotographic recording element as claimed in claim whereinsaid compound is present in an amount within the range of .005 to 1% byweight of the said coating.

recording element as l v 7. An electrophotographic recording element asclaimed in claim 1 wherein R is hydrogen.

8. An electrophotographic recording element as claimed in claim 1wherein the dimer has the formula in-( 311, db

and is present in the said coating on the base sheet with an organicbinder having a specific conductivity of at least 10* ohmcrnf 9. In themethod of preparing copies by electrostatic copy process, the steps ofcharging by corona discharge onto an electrophotographic element havinga transparent to translucent photoconductive coating on a conductivebase sheet in which the photoconductive coating contains an N-alkenylcarbazole dimer having the formula:

in which R is a group selected from the group consisting of hydrogen,alkyl, aryl, cycloalkyl, alkylaryl, cyano, carboxyl and amino and R is agroup selected from the group consisting of hydrogen, alkyl, aryl andcycloalkyl, exposing the charged coating toa light pattern whereby thecharge dissipates from the exposed areas and is retained in theunexposed areas to define a latent electro static image, and thencontacting the image with a developer containing an electroscopicpigment to develop the image.

10. The method as claimed in claim 9 in which the alkenyl carbazoledimer is present in the coating in combination with an organic binderhaving a specific conductivity of at least l0- ohmcm.-

11. The method as claimed in claim 10 in which the coating contains acompound that broadens the spectral sensitivity of the dimer and ispresent in an amount within the range of 0.005 to 1 percent by weight,said compound being a dyestuif selected from the group consisting of atriaryl methane dye, xanthene dye, thiazine dye and acridine dyes 12.The method as claimed in claim 10 in which the coating includes acompound to increase the light sensi tivity of the dimer, said compoundselected from the group consisting of tetracyanoethylene, chloranil, acarboxylic acid, a mineral acid, an acidic metal halide, iodoform,carbon tetrabromide, benzophenone and hydroxy benzophenone, and beingpresent in an amount sufficient to increase the light sensitivity of thedimer.

13. The method as claimed in claim 12 wherein said compound is presentin an amount Within the range of .005 to 1% by weight of the saidcoating.

14. The method as claimed in claim 9 wherein R is hydrogen.

7 15. The method as claimed in c1aim9wherein the dimer organic binderhaving a specific conductivity of at least has the formula v 1 v 10-ohm" cm.- 1

References Cited 5 UNITED STATES PATENTS 1 1 3,037,861 6/1962 Hoegl96-15 25 23 OTHER REFERENCES I5 10 McKinley et al.: J. org. Chem, 31,1963 64 (1966). 0 JOHN C. COOPER III, Pri-ma ry Examiner US. Cl. X.R.

and is present in the coating on the base sheet with an 15 96-16, 1 PC;252--501; 260-315 I UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3,684,506 Dated August 15, 1972 Inventor(s)Anthony J. Guarnaccio and Robert N. Dreyer It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

IN THE SPECIFICATION In column 1, line 34, delete "blank" and inserttherefor blanket Signed and sealed this 29th day of April 1975.

(SEAL) Attest: C. MARSHALL DANN" RUTH C. MASON Commissioner of PatentsArresting Officer and Trademarks

